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MAKE: AudiMODEL: TTYEAR: 2004MILES: 85,000ENGINE: 1.8DESCRIBE ISSUE.... After turning off the car, there is often a small electrical noise (or tiny fan or pump running) for another 5-6 minutes. Wasn't a concern until the noise was super loud after a drive this weekend. When running the car last night and parking it, the softer noise was back. It seems to be coming from the alternator area, but I'm not sure and would appreciate any suggestions. The car does not seem to have any other problems and is in excellent shape.

Check the coolant fan, see if it is still running for a short while. Many cars do keep that fan running after the engine is stopped until the coolant temp is down a bit. If it is changing its sound periodically it may be ready to die from bad bearings. I would be tempted to change a bad fan at the first hint of failure. I am frugal, don't like to change parts "just to be safe", but losing the coolant fan in traffic could overheat the engine and cause very expensive damage.

Only thing I can think of that can make a fan type noise in that area would be the secondary air injection pump. It is located right beneath the alternator. It is basically a fan pushing air in to the exhaust system to allow for better warm up time of the catalytic convertor during a cold start up.

If you doubt that this may be the cause of your problem, you could try removing the relay or fuse for this pump/fan and see if your noise goes away. This will maybe code a OBD2 code however. You seem quite adamant it is NOT the rad cooling fan, so the only other thing I can think of is that. The only other fan in that area, even though they call it a pump.

Now if that is running with the engine off, key off, then you have a serious short to ground there or a problem with the sec air injection being activated that way.

There is also a leak detection pump in the passenger side of the engine bay, but a bit farther removed from the alternator area, and that also is not supposed to ever run engine off, keys in your hands much like the air injection system.

I am merely guessing at something here, and that is, maybe the secondary air pump serves a dual purpose which I did not know about, which may be to cool down the exhaust/turbo system when hotter than normal. It would be logical the audi engineers Incorporated this much like the cooling fans also run for awhile to help cool down the engine after a long hot run as Billr mentioned. But I cannot ascertain this for sure. I have fixed many audi's and volks and benz with the same system and have never heard them run when the engine is off. But I can see my thought as being logical from an engineering aspect and this could be a totally normal behavior if in fact it is the air pump that is creating your noise.

So, try like I said, remove the # 4 fuse in the W relay/fuse box in the engine compartment. That is the fuse for the sec inj air pump. If the noise goes away, you have found the noise. Now is this a normal function? Try calling the dealer cuz I cannot find that this is normal in the description and operation portion of the air injection system in my alldata and no mention of the fan/pump running after the engine is off.

To try to confirm my theory, check for voltage to that fuse key off. If that fuse is not hot at all times, it would impossible for my theory to work as the engineers would not have left that circuit in start/run only if it was not meant to run at any time needed by the ECM when it detects a hot situation. They simply would not have wired it that way.

I hope what I just wrote made sense to you, and maybe someone here can confirm my theory that some times that pump may come into action even when the engine is not running keys in your hand.